The invention relates to a hydraulic solenoid valve with a piston that is displaceable by an armature against the force of at least one return spring and has at least one valve bore which is closable by a valve, preferably, a valve ball, which when the valve is open provides a flow connection between at least one consuming device connection and a reservoir connection of the solenoid valve, whereby the armature in normal operation during displacement in both directions rests at the valve and maintains it in contact with the valve seat.
In this known hydraulic solenoid valve the piston bore is closed by a valve that is held in its closed position by the armature. In the normal operation the armature rests constantly at this valve so that the piston bore remains closed. During operation of such solenoid valves it may happen that the piston jams in its switched position. When the armature then returns into its initial position, the piston may not follow this axial movement of the armature so that the pressure within the consuming device connection remains constant. In order to prevent in this case an overload of the consuming device connected to the consuming device connection the aforementioned valve is provided that because of the returning armature is no longer pressed into its valve seat. Due to the pressure present at the consuming device connection the valve is lifted off its valve seat so that the hydraulic medium can flow back via the now open piston bore to the reservoir connection. In this manner the pressure within the consuming device connection is reduced despite the jammed piston. This safety circuit is very advantageous in an emergency situation, however, it has the disadvantage that the valve during normal operation, i.e., during normal switching processes, can be lifted off the valve seat in an uncontrollable manner, especially when the piston is moved by the return spring. When the valve accidentally is lifted, the hydraulic medium can be ejected in a jet-type manner through the, possibly only partially, opened valve bore. This results in jet forces in the axial direction which act against the return spring and thus result in switching time changes. Furthermore, the sudden lifting of the valve from its seat generates switching noises. These two disturbance factors result in an unsatisfactory pressure and noise behavior.
It is therefore an object of the invention to embody the hydraulic solenoid valve of the aforementioned kind such that an uncontrollable lifting of the valve during normal operation is reliably prevented, but to reliably ensure the safety function of the hydraulic solenoid valve when the piston jams.